The Athena F2's have virtually no competition at the price they're generally selling at now. I've heard from people who've bought them for $300/pair or less.
I can't think of another even decent tower for that money. Since you already have Athena's, you couldn't go wrong stepping up to the larger ones.
That said, there's a better speakers out there, if you're willing to spend the money. How much are you budgeting for the upgrades? I'm not a big fan of Klipsches personally, but some of their newer ones aren't bad at all. But there's a lot of great speakers on the market right now, and it's never been easier to get good sound on a budget than it is today.